Start a Community Garden

Soils and Mulch

 

Soil & Soil Blends

Houston's extended rainy periods and poor clay soils require raised beds and a blended soil mix. Raised beds create positive drainage, provide a healthier soil, and make weeding easier.

Soils differ widely in cost, fertility, ease of weeding, durability, and water and nutrient holding capacity. Most experts find the best soil combines compost with a sandy loam topsoil. You can mix your own soil blend or buy a soil that has already been mixed with compost. Mixing your own requires a good back and a reliable truck. The proportions of compost and sandy loam depend on whether you want a soil that is loose, durable, weed-free, fertile, disease/pest resistant, easy to weed or inexpensive. Soil blends are ready to use when delivered to your site, but can cost more than twice the amount spent on materials you mix yourself.

For a full discussion of soils, see Choosing Soil for Your Garden. Discuss your soil needs with an Urban Harvest staff member. He or she can recommend the best approach for your garden and provide dealer information.

Mulch


You will need to mulch thoroughly to prevent weeds and help plants to better tolerate heat and cold extremes. Weeding is a tedious chore that should always be minimized by keeping your soil covered with a 3 to 4 inch layer of mulch. Mulch will prevent most weed seeds from germinating. Good mulches include hay, composted shredded tree branches (native mulch), and pine needles. Mulching will also maintain soil moisture by reducing evaporation, resulting in lower water bills and less maintenance in the garden.

Choosing Soil for Your Garden


Depending on available funds and labor, you may want to purchase mixed soil or transport river-bank sandy-loam topsoil from a site you are familiar with. The least expensive soils are the soils you gather yourself, while most expensive soils are high quality compost. The general types of soil available are compost/soil blends, pure loam, and sandy soil. Each has advantages and disadvantages. Various garden shops that sell soil in bulk will have their own specific blends: call to find out what is available.


Compost / Soils Blends


Compost is the result of deliberately creating humus, the decomposed remains of plants and soil organisms. The organic acids in humus make soil minerals more available to plants. Roots are best adapted to fully rotted organic matter, so a high humus content is ideal. A soil high in compost will be high in humus and generally, the higher the humus component of the soil, the more fertile it is.

Advantages:

  • The most fertile of all soils, plants grow quickly and well.
  • Its loose, friable structure promotes root development, resulting in better nutrition for plants.
  • There are fewer disease organisms and root nematodes as a result of the higher oxygen and beneficial fungi content of pure compost soil. After a 2 day rain, plant roots are not as likely to have developed diseases.
  • Humus makes nutrients highly available to roots in the same way forests and prairies do naturally.
  • The surface does not crust, so seeds come up easily.
  • Root crops grow well.
  • Heat generated in the process of decomposition destroys most weed seeds introduced through the soil medium.


Disadvantages:

  • Expensive to buy and time-consuming to make.
  • Compost rots continually, so it does need to be replenished seasonally to maintain its beneficial effects.
  • Nitrogen must be added to "compost soils" that are not fully rotted. Nitrogen is consumed in the process of decomposition, so soils which contain products not fully decomposed will rob the soil of nitrogen.


Pure Loam (Topsoil)

Sandy loam topsoil is a material that most farmers are familiar with. Although unusual in urban Houston, it can be found north of town. It can be purchased or trucked in from a sight you are familiar with.


Advantages:

  • Inexpensive.
  • Durable, since it does not rot. Will last indefinitely if you prevent runoff and fertilize.
  • Holds nutrients well.
  • If it is sandy enough, it does not crust over.


Disadvantages:

  • Most likely will contain nutgrass and other weed seeds. If it is a result of river dredging, may contain dollar weed and other water weeds.
  • Must be heat composted with manure to reduce weed seeds.
  • Soil could come from a chemically contaminated site.
  • If soil is not true sandy loam, clay content may be high resulting in difficult weeding. Without added compost or sand, the soil bakes hard and seeds may fail to germinate.
  • Has lower fertility than compost. Without organic matter, it may be low in available nutrients such as phosphorus.
  • Root crops are less productive.
  • Soil has fewer air pockets, resulting in less oxygen available to plants. There are more root fungi diseases and more nematodes. A lack of oxygen can cause problems in wet weather.


Sandy Soil

Although no nutrients are contained in pure sand, many plants will do well in a high sand soil.


Advantages:

  • Inexpensive.
  • Easy to weed.
  • Loose soil texture. Root crops do well.
  • Drains very well, thus preventing root-rots. Melons and sweet potatoes perform well.
  • Easy to cultivate, so you can add organic matter and topsoil easily.
  • Durable. If runoff is prevented and fertility maintained, it will last indefinitely.


Disadvantages:

  • Does not hold water well. More watering is necessary to avoid water stress and to maintain adequate plant nutrition.
  • Holds nutrients poorly, so plants require more fertilizer.
  • Supports high densities of parasitic root worms (nematodes), so plants are less healthy.